fix: Add eslintbot to all_authors.json

`eslintbot` is the default author of the release blog posts. As-is,
after a release, website builds will fail until the person doing the
release replaces their username in the blog post's frontmatter. Is that
a feature? If so, we could provide a friendlier error or perhaps even
have the release process prepopulate it from Jenkins.

This handles the first issue I encountered in
eslint/eslint#16029.

src/_data/all_authors.json

@@ -119,5 +119,16 @@
         "twitter_username": null,
         "github_username": "mdjermanovic",
         "location": null
+    },
+    "eslintbot": {
+        "username": "eslintbot",
+        "name": "ESLint Bot",
+        "title": "Guest Author",
+        "website": "https://eslint.org",
+        "avatar_url": "https://avatars.githubusercontent.com/u/13383618?v=4",
+        "bio": null,
+        "twitter_username": "geteslint",
+        "github_username": "eslintbot",
+        "location": null
     }
 }